1. Field of the Invention
The present invention relates to radar systems and, more particularly, to improvements in sidelobe blanking systems for radar systems.
While the present invention will be described herein with reference to particular embodiments, it will be understood that the invention is not limited thereto. The principles of this invention may be adapted and employed to meet a variety of requirements as those of ordinary skill in this art will recognize in light of the present disclosure.
2. Description of the Prior Art
Quite often, airborne and radar missile systems must operate in environments where in addition to radar returns from airborne targets to be detected, numerous returns are received from highly reflective ground objects in the main antenna sidelobes. Sources of such returns include terrain irregularities and man-made structures or vehicles. The returns through the main antenna sidelobes frequently produce false airborne target detections, i.e., detections which cannot be distinguished from airborne targets. Thus, effective operation of airborne radar system requires a method of discriminating between the desirable airborne targets whose returns are received through the antenna's mainlobe and the undesirable returns which are received through the main antenna side lobes.
To resolve this problem, some airborne radar systems have employed radar receivers which incorporate a guard channel in addition to the main channel to obtain at least a partial discrimination between desirable and undesirable targets.
A typical sidelobe blanking receiver utilizes an auxiliary or guard antenna to receive the sidelobe signals. The sidelobe signals are processed in the sidelobe receiver in an identical manner to the processing of the signals in the main radar receiver. The guard antenna's spatial coverage substantially matches that of the radar antenna sidelobe pattern with the exception that it has a higher gain configuration. The detected outputs of the two receivers are then compared. If the amplitude of the video from the sidelobe receiver exceeds the amplitude of the radar receiver video, the signal is known to have been received by the sidelobes of the main antenna. A tracking radar receiver can then ignore pulses with that pulse repetition frequency. However, if the amplitude of the radar receiver video exceeds that of the sidelobe receiver video, the target is assumed to be in the main beam and not in the sidelobes. This check is especially important to a tracking radar during initial lock-on.
The necessity for a separate radar receiver adds significantly to the expense of conventional sidelobe blanking systems. Thus it is an object of the present invention to provide a sidelobe blanking system that does not require a separate radar receiver.
Those skilled in the art have come to recognize that encoding the outputs of the main and guard antennas and phase related signals, provides signals which are easier to store and work with. See for example Radar Handbook, Merrill I. Skolnik, McGraw-Hill Book Co., 1970, Library of Congress Catalog Card #69-13615, pps. 5-40, 5-41. However, the advantages of this approach have not heretofore been fully realized because the phase error between the guard and main antennas varied for every target as a function of target spatial angle. Thus, it is a still further object of the present invention to provide a sidelobe blanking system which does not require a separate radar receiver, and allows for phase detection, sidelobe blanking while compensating for variable phase error between the main and guard antennas.